From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9C191C433F5 for ; Tue, 10 May 2022 03:37:46 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3961E6B0073; Mon, 9 May 2022 23:37:46 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3442A6B0074; Mon, 9 May 2022 23:37:46 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 2341E8D0001; Mon, 9 May 2022 23:37:46 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 1610E6B0073 for ; Mon, 9 May 2022 23:37:46 -0400 (EDT) Received: from smtpin29.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id DD92011F8 for ; Tue, 10 May 2022 03:37:45 +0000 (UTC) X-FDA: 79448424090.29.5475189 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf22.hostedemail.com (Postfix) with ESMTP id DAE74C0086 for ; Tue, 10 May 2022 03:37:43 +0000 (UTC) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 6B9AE616E2; Tue, 10 May 2022 03:37:44 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 92A64C385A6; Tue, 10 May 2022 03:37:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1652153863; bh=FT1lNXjVudXrHCOQvlF/y7rn0xd5iMFFhyFSFgCjpK8=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=i7mp2aVnHO4vcEj4mBltGUfoGij1uuMJVZCX9l9QX/uC7NbDvWvqoMlDvRCEft3dZ 1jnk2UYARlP0RJ/Zru5mnO2/xVPCJQODn/vgiagQ4+wTUxNTgB01HTAd4R8KOMu4m1 B+CwEerU2QJUc/d7dJlZr3QcDx8Ig8PUYlmQ2aEI= Date: Mon, 9 May 2022 20:37:42 -0700 From: Andrew Morton To: "Matthew Wilcox (Oracle)" Cc: Kees Cook , linux-mm@kvack.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH 1/4] mm/usercopy: Check kmap addresses properly Message-Id: <20220509203742.0f4adfa4004e51e66c1c9a20@linux-foundation.org> In-Reply-To: <20220110231530.665970-2-willy@infradead.org> References: <20220110231530.665970-1-willy@infradead.org> <20220110231530.665970-2-willy@infradead.org> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Stat-Signature: 3f7emk7nbjtgfnmmmja9778g63ut5iy6 X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: DAE74C0086 Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=linux-foundation.org header.s=korg header.b=i7mp2aVn; spf=pass (imf22.hostedemail.com: domain of akpm@linux-foundation.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org; dmarc=none X-Rspam-User: X-HE-Tag: 1652153863-679547 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, 10 Jan 2022 23:15:27 +0000 "Matthew Wilcox (Oracle)" wrote: > If you are copying to an address in the kmap region, you may not copy > across a page boundary, In the source, the destination or in both, and why may we not? > no matter what the size of the underlying > allocation. You can't kmap() a slab page because slab pages always > come from low memory. Why not? kmap() does if (!PageHighMem(page)) addr = page_address(page); else addr = kmap_high(page);